Positioning control system for a machine that performs work on a moving part

ABSTRACT

A programmable and manually operable control system for controlling the position of a machine relative to a workpiece so the machine may perform work at various locations on the workpiece while the workpiece is moved by the conveyor. The system includes a pair of synchro resolvers which provide output signals indicative of the position of the machine relative to a datum position and a pair of synchro resolvers which provide output signals indicative of the position of the conveyor relative to the datum position. The outputs of the machine indicating resolvers provide the inputs to the conveyor indicating resolvers and the outputs of the conveyor indicating resolvers are compared with command signals that are generated by a continuously recycling counter which has been preset by signals from a memory so the displacement between selected locations on the workpiece and the machine is electrically measured without using differential mechanical gearing. The control system is arranged so the machine will move synchronously with the workpiece, independently of the workpiece, and synchronously with the workpiece while the machine is moving from one preprogrammed location to a new preprogrammed location on the workpiece.

United States Patent [151 3,686,556 Anger et a]. 1 Aug. 22, 1972 [54]POSITIONING CONTROL SYSTEM FOR A MACHINE THAT PERFORMS WORK ON A MOVINGPART Assignee: Square D. Company, Park Ridge, Ill. Filed: May 24, 1971Appl. No.: 146,110

US. Cl. ..318/595, 318/603, 318/605 Int. Cl. ..G05b 11/18 Field ofSearch ..318/595, 600, 605, 603

[56] References Cited UNITED STATES PATENTS 6/ 1962 Fitzner ..3 18/594 X8/ i962 Galman ..3 18/595 X 9/ l 964 Fisher ..318/592 3,040,22l3,051,942 3,l 5 l ,282

Primary Examiner-Benjamin Dobeck AtmrneyHar0ld .l. Rathbun and WilliamH. Schmelmg ABSTRACT A programmable and manually operable control systemfor controlling the position of a machine relative to a workpiece so themachine may perform work at various locations on the workpiece while theworkpiece is moved by the conveyor. The system includes a pair ofsynchro resolvers which provide output signals indicative of theposition of the machine relative to a datum position and a pair ofsynchro resolvers which provide output signals indicative of theposition of the conveyor relative to the datum position. The outputs ofthe machine indicating resolvers provide the inputs to the conveyorindicating resolvers and the outputs of the conveyor indicatingresolvers are compared with command signals that are generated by acontinuously recycling counter which has been preset by signals from amemory so the displacement between selected locations on the workpieceand the machine is electrically measured without using differentialmechanical gearing. The control system is arranged so the machine willmove synchronously with the workpiece, independently of the workpiece,and synchronously with the workpiece while the machine is moving fromone preprogrammed location to a new preprogrammed location on theworkpiece.

18 Claims, 10 Drawing Figures P7P A SEQUENCE MEMORY ,3] H? TOR CONTROLLUNTRLH MODULE 1 l MODULE 35 i 36 37 GATES GATES GATES 341' F 3 1 38 4o1 [41 r HOLD JOG couwiimo c wffin Fumno" r iiii r io u TIMING MODULEMODULE MODULE "WULE MODULE MODULE 54 44 INTEGRATOR I 57 E 52 SWiTCH SWT" 3" (i MODULE cuMp ro l SI -4C v c SIN/ C05 I GENERATOR 48 56 SWITCH IDECEL. MODULE cos g L g MODULE MODULE INTEGRATOR 47 58 l 1 60 \55 USWITCH FINE MODULE COMPARATOR Patented Aug. 22, 1972 3,686,556

6 Sheets-Sheet f;

500 KHZ REF JXK'EL TQ'R ERNEST G. ANGER G|LE$ J. RICHARDS 2 JOHN FBLOODGOOD 5y ROY r. GEIGER Patented Aug. 22, 1972 6 Sheets-Sheet 4uJDoOS 0: 1 A'EQQMK. H w ERNEST s. ANGER T T GILES J. RICHARDS JOHN FBLOODGOOD mum mmu N1 00m mum NIxOOm NIS- Patented Aug. 22, 1972 6Sheets-Sheet b 2% H M 8m w w u www t m .m

m QE

OmZ

ERNEST G. ANGER GILES J. RICHARDS JOHN E BLOODGOOD ROY J. GEIGERPatented Aug. 22, 1972 6 Sheets-Sheet 6 FIG.6

wh40 mum DISPLACEMENT FIG.6B

FIG. 6A

FIG. 6D

I :N'VEN'TOR.

ERNEST G ANGER GILES J. RICHARDS JOHN F. BLOODGOQD B ROY J. GEIGER W I bd.

POSITIONING CONTROL SYSTEM FOR A MACHINE THAT PERFORMS WORK ON A MOVINGPART The present invention relates to positioning control, and moreparticularly to a control system for positioning a machine at desiredpositions along a workpiece while the workpiece is moving along apredetermined path relative to a datum position.

In the field of positioning control, various systems have been proposedfor moving a controlled member in accordance with instructions storedwithin a memory so that work may be automatically performed upon aworkpiece. In these prior systems, the maximum range of movement of thecontrolled member is usually limited to a few feet and generally theworkpiece is maintained stationary while work is performed by thecontrolled member. Thus the systems as heretofore known are notparticularly suited to control the positioning of a machine whichperforms work at various positions along the entire length of the bodyof an automotive vehicle while the body is transported by a movingconveyor through a work station.

A technique commonly practiced in factories which manufacture orassemble mass-produced automotive vehicles requires that the componentsof the subassemblies for a complete vehicle be assembled to each otherwhile the components are carried by a suitable support that is moved bya conveyor past the various work stations where parts are secured toeach other to complete the subassembly. For example, the fabrication ofa subassembly, called the body of the vehicle, is normally accomplishedby accurately positioning the components on a fixture, called a bodytruck, and moving the body truck past work stations where the parts ofthe body are welded together. The welding of the parts is accomplishedby welding guns which are manually moved to the desired positions alongthe body parts to secure the parts together by a series of spot weldswhich are sequentially formed as the gun is positioned at spacedlocations along the body parts. While the manual formation of spot weldshas proven satisfactory, it is objectionable in that it not only dependsupon the skill of the gun operator to accurately locate the welds and toassure that the proper number of welds are made between the parts, butit also occasionally requires the operator to assume physicallyuncomfortable and exhausting positions to make the welds.

While it is apparent that the machine as controlled by the controlsystem as will be hereinafter described may be readily modified toperform a variety of operations upon workpieces while the workpieces aremoving along a predetermined path, the control system is described ascontrolling the positioning of a resistance welding gun to form spotwelds between parts of an automotive vehicle body as the body parts aretransported by a moving body truck along a conveyor line. One of theproblems presented in synchronizing the operation of a machine with theposition of parts carried on a conveyor is that, conventionally, thespeed of the conveyor which moves the parts is not closely controlled.Another problem presented in using machines to perform work on bodyparts which are carried on a moving conveyor in an automotive vehiclefactory is that to maximize production, it is imperative that theconveyor move continuously. This means that any malfunction of a machinewhich would require the conveyor to be stopped would be highlyobjectionable. One type of failure or malfunction which may occur in aresistance spot welding apparatus is the weld electrodes may be stuck tothe parts which are being welded together. When this type of failureoccurs and the apparatus is being manually operated, minimaldifficulties result as the human operator merely moves along the lineuntil the welding electrodes are freed from the body part. However, whenthis type of failure occurs in a machine controlled welding apparatus,more disasterous consequences may occur because of the capability of themachine to pull the parts from their position on the body truck or tomutilate the parts beyond use.

To successfully perform work upon a workpiece carried by a conveyor, amachine which performs the work must be capable of operating in severalmodes. In one mode of operation, the machine must be capable of movingupstream and independently of the conveyor to a position where it waitsfor a part to enter the work station and then move with the part topreprograrnrned positions on the part where it performs its work as thepart is moved through the work station. In another mode of operation,the machine must be capable of having its movements manually controlledwhen the conveyor is stationary. In another mode of operation, themachine must be capable of moving synchronously with the part as thepart moves through the work station.

It is to be appreciated that while the control, as will be hereinafterdescribed, is concerned with the positioning of a machine along alongitudinal axis relative to a part that is carried by a movingconveyor, a multiple axis control of the machine, i.e., six axiscontrol, may be readily obtained by duplicating the necessary componentsof the control for the longitudinal axis with the exception that thesynchro revolvers, which are used to synchronize the movement of themachine with the movement of the conveyor, are eliminated.

It is an object of the present invention to provide a control system fora machine which will automatically perform work on workpieces that arecarried on a moving conveyor.

Another object is to provide a control system for a machine which willcontrol the position of the machine relative to preselected positions ona part so the machine may perform work on the part while the part ismoved by the conveyor.

A further object is to provide a control system for positioning amachine at desired positions along a workpiece while the workpiece ismoving along a predetermined path relative to a datum position with ameans for electrically synchronizing and controlling the movement of themachine with respect to the movement of the workpiece.

An additional object is to provide a control system for positioning amachine at desired positions along a workpiece while the workpiece ismoving along a predetermined path relative to a datum position with ameans for electrically synchronizing the movement of the machine withrespect to the workpiece, with said synchronizing means including afirst pair of synchro rewlvers which provide an output indicative of theposition of the machine relative to the datum position, a second pair ofsynchro resolvers which provide an output indicative of the position ofthe workpiece relative to the datum position, a means which is arrangedto be energized by the output of the first pair of resolvers and providean input to the second pair of resolvers and a means which is arrangedto compare the outputs of the second resolvers with recycling commandposition signals and cause the command signals to correspond with theoutputs of the second pair of resolvers when the machine is required tomove synchronously with the workpiece along the path of movement of theworkpiece.

A still further object is to provide a control system for positioning amachine at desired positions along a workpiece while the workpiece ismoving along a predetermined path relative to a datum position with ameans for electrically synchronizing the movement of the machine withrespect to the workpiece that includes a pair of synchro resolvers eachof which provides an output indicative of the position of the machinerelative to the datum position, a second pair of synchro resolvers eachof which provides an output signal indicative of the position of theworkpiece relative to the datum position, a means for causing the inputsof the second pair of resolvers to be energized by the outputs of thefirst pair of revolvers and a means which compares both the order ofoccurrence and the interval between the occurrence of the output signalsof the second pair of resolvers and a command signal and provides anerror signal which has a magnitude dependent upon the interval betweenthe signals and a direction indication controlled by the order ofoccurrence of the signals.

A still further object is to provide a control system for positioning amachine at desired positions along a workpiece while the workpiece ismoving along a predetermined path relative to a datum position with ameans for electrically synchronizing the movement of the machine withrespect to the workpiece that includes a pair of synchro resolvers eachof which provides an output indicative of the position of the machinerelative to the datum position, a second pair of synchro resolvers eachof which provides an output signal indicative of the position of thework piece relative to the datum position, a means for causing theinputs of the second pair of resolvers to be energized by the outputs ofthe first pair of resolvers and a means which compares both the order ofoccurrence and the interval between the occurrence of the output signalsof the second pair of resolvers and a command signal and provides anerror signal which has a magnitude dependent upon the interval betweenthe signals and a direction indication controlled by the order ofoccurrence of the signals and to provide the control with a means whichis manually operable to cause the machine to move independently of thesignals.

Another object is to provide a control system for positioning a maclnineat desired positions along a workpiece while the workpiece is movingalong a predetermined path relative to a datum position with a meanswhich provides a feedback signal that is indicative of the relativepositions of the workpiece and the machine relative to the datumposition, a means including a recycling counter which provides a commandsignal phase that is preset to be indicative of a preselected positionon the workpiece at which the machine is to be positioned while theworkpiece is moving relative to the datum position and a hold meansresponsive to the feedback signal for causing the output of the counterto correspond to the feedback signal during periods when the hold meansis activated.

An additional object is to provide a control system for positioning amachine at desired positions along a workpiece while the workpiece ismoving along a predetermined path relative to a datum position with ameans which provides a feedback signal that is indicative of therelative positions of the workpiece and the machine relative to thedatum position, a means including a counter which provides a commandsignal that is indicative of a preselected position on the workpiece atwhich the machine is to be positioned while the workpiece is movingrelative to the datum position, a jog means for causing the machine tomove at either of two selected speeds independently of the workpieceswhen the jog means is activated, said jog means including circuitry thatis responsive to the feedback signal for causing the output of thecounter to correspond to the feedback signal during periods when the jogmeans is activated and a means which will cause the movement of themachine to increase at a preselected rate when the jog means is actuatedand to abruptly decrease when the job means is deactivated.

A further object is to provide a control system for positioning amachine at desired positions along a workpiece while the workpiece ismoving along a predetermined path relative to a datum position with ameans which provides a feedback signal that is indicative of therelative positions of the workpiece and the machine relative to thedatum position, a means including a counter which provides a commandsignal that is indicative of a preselected position on the workpiece atwhich the machine is to be positioned while the workpiece is movingrelative to the datum position and a jog means for causing the machineto move independently of the workpieces when the job means is activated,said jog means including circuitry that is responsive to the feedbacksignal for causing the output of the counter to correspond to thefeedback signal during periods when the jog means is activated.

Another object is to provide a control system for controlling theenergization of an electric motor which drives a machine to desiredpositions along a workpiece while the workpiece is moving along apredetermined path relative to a datum position with a means whichprovides a feedback sigial that is indicative of the relative positionsof the machine and workpiece relative to the datum position, a meanswhich provides a command signal that is indicative of a preselectedcommanded position on the workpiece at which the machine is to bepositioned, said feedback and command signals consisting of apredetermined voltage change which occurs at predetermined instantsduring each cycle of a reference wave and respectively varying in timeduring each cycle depending upon the relative positions of the machineand workpiece from the datum position and the location of the desiredposition relative to the datum position, means for comparing both theorder of occurrence and the interval between the occurrence of thevoltage changes of the feedback and the command signal and providing anoutput signal pulse during each half cycle which has a width dependentupon the interval between said pulses and a polarity indicative of theorder of occurrence of the pulses, and a deceleration means forcontrolling the direction of rotation and the speed of rotation of themotor in response to the polarity and width of the pulses, saiddeceleration means being arranged to exponentially increase the ratiobetween the width of the pulses and the energization of the motor as thewidth of the pulses decreases during periods when the machine is slowingdown as the machine is approaching the commanded position.

Further objects and features of the invention will be readily apparentto those skilled in the art from the following specification and fromthe appended drawings illustrating certain preferred embodiments, inwhich:

FIG. 1 shows in block diagram form a control system embodying thefeatures of the present invention.

FIG. 2 is a schematic and block diagram of the circuitry used to comparethe outputs of the position detecting resolvers and the command positionsignal provided by the components in FIG. 1.

FIG. 3 is a graphical representation showing the time relationships ofsignals in the circuit shown in FIG. 2.

FIG. 4 is a schematic and block diagram of the circuitry used to causethe machine in FIG. 1 to operate in a hold position and/or a joggingmode of operation.

FIG. 5 is a schematic diagram of the circuitry used to control theenergization and de-energization of a drive motor for the machine inFIG. 1 when the jogging mode of operation is initiated and terminated.

FIG. 6 is a schematic diagram of a circuit which controls theenergization of the drive motors for the machine in response to theoutput signal from the comparator circuit in FIG. 1.

FIGS. 6A and 6B are graphs illustrating the change in the energizationof the drive motor for a machine in FIG. 1 as the machine moves toward acommanded position.

FIGS. 6C and 6D are graphs with time as a reference, illustrating themanner in which a capacitor in FIG. 6 is charged in response to errorpulses.

Referring now to the drawings, and more particularly to FIG. 1 thereof,the control system of the present invention is therein illustrated ascontrolling the position of a machine 10 relative to the position of apair of workpieces 11 and 12, which represent parts of an automotivevehicle body, that are carried on a longitudinally movable fixture,known in automotive assembly plants as a body truck 13. In conventionalpractices, as followed in automotive assembly plants, a succession ofspaced trucks 13 are continuously moved along a path dictated by a pairof spaced rails 14 past work stations where work is performed on theparts carried by the trucks. Each of the trucks 13, as used with thepresent system, has a block 15 secured at one of its longitudinal sideswith an opening 16 accurately located in the block 15 relative to theworkpieces 1 1 and 12. The opening 16 is located to receive a pin 17that projects upwardly from a longitudinally movable chain 18 which ismoved by the truck 13 horizontally along a path parallel to the rails 14in the direction indicated by the arrow 19 as the truck 13 moves from anupstream end 20 of the work station, wherein the machine 10 is located,to the downstream end 21 of the work station. The chain 18 is arrangedso that as a truck 13 enters the upstream end 20 of the work station,the pin 17 will be projected upwardly, by a means not shown, into theopening 16 to cause the chain as well as the pin 17 to be moved by thetruck 13 downstream to the end 21 whereat the pin 17 is retracted fromthe opening 16 in the block 15 as the truck 13 carrying the fabricatedworkpieces 11 and 12 leaves the work station, so that the chain 18,including the pin 17 may be moved by a means, not shown, upstream to theupstream end 20 where it will be in a position to engage a block 15 on asubsequent truck 13, as the truck 13 enters the work station.

The machine 10 includes a base 22 that is movable along the parallelrails 23 along a path that is parallel and spaced from the path ofmovement of the truck 13. The base 22 is moved by a lead screw 24through a suitable travelling nut, now shown, which is secured to thebase 22 and arranged to be driven by the lead screw 24. The lead screw24 is rotated through a suitable speed reducing gear box 25 by anelectric motor 26. A vertical stanchion 27, which is secured on the base22, supports an arm 28. The arm 28 is supported by the stanchion 27 sothat the arm 28 may move horizontally along a horizontal axis thatextends vertically to the path determined by the rails 14 and rotateabout its horizontal axis. Secured on the free end of the arm 28 is apair of electrodes, indicated as 29, which are arranged to engage andspot weld the workpieces 11 and 12 together. The electrodes 29 aremovable by a suitable mechanism 30 in an arcuate path along a verticalaxis as well as an arcuate path that extends horizontally. Thehorizontal arm 28 is also movable along a vertical axis on the stanchion27. Thus the movement provided by the base 22 along the axis dictated bythe rails 23, the vertical, horizontal and rotational movementof the arm28 about the stanchion 27 and the movement provided by the mechanism 30on the end of the arm 28 about the horizontal and vertical axes, willpermit electrodes 29 to move along six axes relative to the workpieces11 and 12.

A system which will control the horizontal positioning of the machine 10along an axis parallel to the movement of the body truck 13 and theworkpieces 11 and 12 includes a memory 31 which is preferably of theretentive type so that information stored therein will not be lost inthe event of a power failure. The memory 31, as used herein, is acommercially available type, and includes an array of bistable statemagnet cores which are capable of being programmed to have informationstored therein. The information which is stored in the cores of thememory 31 includes positional infon mation which will dictate thedesired positions of the welding electrodes 29 relative to theworkpieces 1 l and 12, functional information which controls theoperation of the welding electrodes, information which will controlother mechanisms of the machine, such as operating solenoids and thelike, and program information which will indicate that the programmedwork for any particular type of parts 11 and 12, which may be mounted onthe body truck, has been completed.

The operation of the control system is dictated by suitable circuitrywithin an operator control station module 32 which supplies inputsignals to a sequence control circuit module 33 and a hold-jog circuitmodule 34. While the control module 32 may be programmed to cause thecontrol system to operate the machine 10 in modes other than are hereindescribed, for purposes of understanding of the operation of thecircuits which will be later described, the control module 32 isdescribed as providing suitable output signals which will cause themachine to operate in an automatic mode, an indexing mode, a teach andjogging mode and a mode designated as hold.

The control module 32, when programmed to cause the machine to operatein the index or automatic mode, will provide signnal inputs to thesequence control module 33 which will cause the digital commandinformation stored within the memory 31 to be read out through gates 35,36 and 37 and be respectively supplied as input information to a coarsecommand counter 38, a fine command counter 39, circuits within afunction module 40 and circuits within an end of program andmiscellaneous function module 41. The counter 38 and 39 are 1,000 bitrecirculating counters and receive a continuous train of 500 KHZreference input pulses from a system timing module 42. When thecontinuous train of 500 KHZ pulses is fed into the counters 38 and 39and the counters 38 and 39 are reset by the reference input pulses andpreset by the information from the memory 31, the train of 500 HZ pulseswill appear at the output of the most significant bit of the counters 38and 39 which will have a predetermined phase relationship with respectto a 500 HZ reference input signal pulses and thereby in effect divideeach cycle of the 500 HZ input signal into 1,000 distinct commandpositions.

A position responsive means which provides a signal indicative of theposition of the machine 10 relative to a datum position 43, locatedequidistant between the ends and 21, includes a coarse feedback resolver44 and a fine feedback resolver 45. Similarly, a position responsivemeans which will provide a signal indicative of the position of the pin17 relative to the datum position includes a coarse feedback resolver 46and a fine feedback resolver 47. Each of the resolvers 44-47 is asynchro-type resolver and includes a rotatable shaft, a pair of inputwindings wound in spaced quadrature and an output winding that providesa cyclic output voltage signal which varies in phase relative to thephase of the voltage across its input windings with the angular position of the shaft when the input windings are respectively energizedfrom an alternating current source by equal magnitude alternatingvoltages that are in quadrature.

The shaft of the coarse feedback resolver 44 is connected through a gearbox 48 to be rotated by the lead screw 24 one complete revolution whenthe machine 10 is moved twice the distance between the ends 20 and 21.The shaft of the fine feedback resolver 45 is connected through a gearbox 49 to be rotated by the lead screw 20 revolutions for eachrevolution of the shaft of the coarse resolver 44. The shaft of thecoarse feedback resolver 46 is connected through a gear box 50 to berotated in response to the movement of the chain 18 one completerevolution when the pin 17 is moved twice the distance between the ends24) and 21. Similarly, the shaft of the fine resolver 47 is connectedthrough a gear box 51 to be rotated in response to the movement of thechain 20 revolutions for each revolution of the shaft of the coarseresolver 46.

A sin/cos generator circuit module 52, which is controlled by the timingmodule 42, supplies one of the input windings of the resolvers 44 and 45with a 500 HZ sine wave input that is in phase with the 500 HZ referencesine wave input to the counters 38 and 39 and the other of the pair ofinput windings of the resolvers 44 and 45 with a 500 HZ sine wave ofequal amplitude, but lagging the reference sine wave by 90 (cos). Withthis excitation, the outputs of the resolvers 44 and 45 will vary inphase relative to the reference sine wave with the position of theirrespective shafts. The 500 HZ sine wave output of the resolver 44 issupplied as an input through a lead 53 to one of the windings of theresolver 46 and is integrated by an integrator circuit module 54 andsupplied to the other input winding of the resolver 46 as a 500 HZ sinewave of equal amplitude, but lagging in phase by 90 (cos) with theexcitation voltage supplied by the lead 53. Similarly, the 500 HZ sinewave output of the resolver 45 is supplied as an input through a lead 55to one of the pair of input windings of the resolver 47 and is integrated by a circuit module 56 and supplied to the other input of thewinding of the resolver 47 as a 500 HZ sine wave of equal amplitude butlagging in phase by (cos) with the excitation voltage supplied by thelead 55.

The 500 HZ sine wave outputs from the resolvers 46 and 47 arerespectively amplified, clamped and rectified by circuits within switchmodules 57 and 58 to appear as a pulse train that is similar to theoutputs of the coarse command counter 38 and the fine command counter39. The outputs of the switch modules 57 and 58, which are respectivelycalled a coarse feedback signal CFB and a fine feedback signal FFB, aresupplied as inputs to a coarse comparator module 59 and a finecomparator module 60, which also respectively receive inputs from thecoarse command counter 38 arnd the fine comrrnand counter 39.

The output of the coarse command counter 38, hereinafter referred to asa coarse command signal CC, is a logic "1" to 0 transition at thetrailing edge of each cycle of the 500 HZ voltage wave. The 1 to 0signal change can be made to occur at any one of 1,000 differentinstants during each cycle of the 500 Hz reference voltage wave so thatthe coarse command counter 38 can be programmed to provide 1,000distinct coarse command signals for each revolution of the coarseresolver 44 or 46. Similarly, the fine command counter 39 can beprogrammed to provide 1000 distinct command l to 0 logic signals, orfine command signals FC, for every one-twentieth revolution of thecoarse resolver 44 or 46. Therefore, if it is assumed that the totaldistance between the ends 20 and 21 is 200 inches and both the machine10 and the truck 13 are capable of moving 200 inches, then the relativerange of movement between the workpieces 11 and 12 and the electrodes 29will be 400 inches. Thus as the coarse command counter 38 is capable ofproviding 1,000 distinct coarse command signals over the entire range ofmovement (one revolution of the coarse resolvers 44 and 46) which is 400inches, and the fine command counter 39 is capable of providing 1000distinct tine command signals over one-twentieth of the total range (20inches), the linear axis will have a resolution of 0.02 inches and thesystem has the capability of 9 being programmed to 20,000 distinctcommand positions within the 400 inch range of relative movement betweenthe machine 10 and the truck 13.

As will be later described, the circuitry within the coarse comparator59 compares the coarse feedback signal CFB with the coarse commandsignal CC and provides an output error signal to a switch module 61which is dependent upon the order of occurrence and the time intervalbetween the l to 0 change in the signals from the compared signals whichwill cause the motor 26 to be energized to rotate either in the forwardor reverse directions, depending on the order of occurrence of the l to0" signals at a predetermined rate when the time interval between thesignals is greater than a preselected interval. Also, the finecomparator 60 compares the fine feedback signal FFB with the finecommand signal FC and provides an output error signal to the switchmodule 61 which is dependent on the order of occurrence and the intervalbetween the l to 0" change in the signals which it compares. The outputerror signal from the fine comparator 60 to the switch module 61 willcause the motor 26 to be energized to rotate in the forward or reversedirections depending upon the order of occurrence of the l" to 0 signalchanges of the compared signals at a rate dependent upon the magnitudeof the interval between the signal change of the compared signals.

The output of the switch module 61 is supplied as an input to adeceleration module 62, which will be later described. The module 62converts and modifies the output pulses from the switch module 61 to apositive or negative filtered DC. voltage which is supplied as an inputto a servo-drive amplifier 63 which in turn controls the energization ofthe motor 26. if desired, the drive amplifier 63 may also be furnishedwith an input signal from a tachometer 64 that is driven by the motor 26to limit the energization of the motor 26.

The motor 26, when energized, will rotate the lead screw 24 through thegear box 25 to move the electrodes 29 which are supported by the base 22and rotate the shafts of the resolvers 44 and 45 in a direction whichwill reduce the error signals as detected by the comparators 59 and 60.When the electrodes 29 are in their commanded position relative to theworkpieces 11 and 12, the l to 0 signal changes of the coarse feedbacksignal CFB and the coarse command signal CC will be in phase and the 1to "0 signal change of the fine feedback signal FFB will be in phasewith the fine command signal PC which will cause the switch module 61 tosupply an in position signal to the logic circuitry within an end ofmotion module 65. The module 65 in response to the in position inputsignal supplies a signal to the function module 40 which will initiatethe operation of a weld sequence timer and cause the electrodes 29 tospot weld the workpieces 11 and 12 together. During the weld interval,when the spot weld is being formed, the workpieces l1 and 12 will bemoving through the work station and the feedback outputs of the coarseand the fine resolvers 46 and 47 will be continuously chanp'ng. The finecomparator 60, in response to the changing fine feedback signal FFB,will provide an output through the circuits in the switch module 61 andthe deceleration module 62, which causes the servo-drive amplifier 63 toprovide the motor 26 with an energization that is exactly sufficient tomove the machine 10 synchronously with the truck 13. The synchronousmovement of the machine 10 causes the coarse and fine resolvers 44 and45 to supply a changing input to the coarse and fine resolvers 46 and 47which in turn reduces the changing coarse and fine feedback signal inputto the comparators 59 and 60 so that the welding electrodes 29 remain intheir programmed position as they are forming a spot weld between theworkpieces 11 and 12.

The function module 40, at the end of the weld interval, will supply aninput through the lead 66 to the sequence control module 33 which causesthe sequence control module 33 to sequence the memory 31 and open thegates 35-37 to reprogram the coarse and the fine command counters 38 and39, and the function module 40, so that the command counters 38 and 39provide output command signals which will require the machine 10 to moveto a new preprogrammed position relative to the workpieces 1 l and 12.The coarse and fine comparators 59 and 60 in response to the changedcoarse'and fine command signal will provide an output signal which willcause the motor 26 to be energized to reduce the error signal in amanner previously described as the machine 10 moves to its newlycommanded position relative to the workpieces 11 and 12.

At the end of the program, that is, when all the required spot weldshave been made between the parts 11 and 12 at the positions dictated bythe information stored within the memory 31, the end of program module41 will supply a signal through a lead 67 to the switch modules 57 and58. Also at the end of the program, the memory 31 will supply suitableinputs through the gates 35 and 36 to the coarse and fine commandcounters 38 and 39 which will cause the counters to supply coarse andfine command signals which will require the machine 10 to move upstreamto its start position at the end 20 where it will await the entry of asubsequent truck 13 carrying unassembled workpieces into the workstation. The circuitry within the switch modules 57 and 58 is arrangedso that a signal input from the module 41 will cause the switch modules57 and 58 to respond to the outputs of the resolvers 44 and 45 insteadof the outputs from the resolvers 46 and 47 and permit the machine 10 tomove independently of the chain 18 upstream to the end 20. During themovement of the machine 10 to the end 20, the truck 13 carrying theassembled workpieces will continue to move toward the end 21. The pin 17is disengaged from the opening 16 when the truck 13 leaves the workstation at the end 21, so that the chain 18 may be moved upstream andposition the pin 17 at the end 20 where it will engage the opening 16 ina subsequent truck 13 as the subsequent truck 13 enters the workstation.

The foregoing operation constitutes a description of the operation ofthe control system when the control module 32 is programmed so that themachine 10 will operate in the automatic mode. The indexing mode ofoperation is provided in the control system to check the informationstored within the memory 31 during periods when the conveyor which movesthe body truck 13 is stopped. The program within the memory 31 may bechecked by merely pressing a button in the control module 32 which willcause the machine 10 to move from one preprogrammed position to its nextprogrammed position and maintain its position until the indexing buttonis again depressed, which will sequence the memory 31 one step andrequire the machine 10 to move to a new position. Thus the machine 10may be sequenced through its programmed steps to determine if theinformation within the memory 31 corresponds to a program which willlocate the spot welds between the workpieces l l and 12 at their desiredlocations.

A hold mode of operation is included in the control system to damageswhich could occur in event an emergency should occur while the machine10 is operating in its automatic mode and it becomes necessary to stopthe conveyor line which moves the trucks 13. The hold mode of operationmay be initiated at any time by activating a suitable hold switch in thecontrol module 32. If the machine 10 is moving toward a new position onthe workpieces 11 and 12, when the hold mode of operation is initiated,the coarse and fine command signals will be reset to correspond to thecoarse and fine feedback signals, in a manner to be later described indetail, and the movement of the machine 10 will be synchronized with themovement of the conveyor as the conveyor coasts to a stop.

The initiation of the hold switch will cause the holdjog module 34 tosupply a signal for a brief time interval, i.e., 380 milliseconds, tothe comparators S9 and 60 which will block the operation of thecomparators 59 and 60 and cause the comparators 59 and 60 to supply azero output error signal which will permit the motor 26 to decelerate.During the 380 millisecond time interval, the Hold-jog module 34, inresponse to feedback signals from the resolvers 46 and 47, will supplyinput signals to the counters 38 and 39 which will preset the counters38 and 39 when the coarse and fine feedback signals change from 1" to sothat the coarse and the fine command signals will be in phase with thecoarse and the fine feedback signals. The presetting of the counters 38and 39 will occur approximately 190 times during the 380 millisecondinterval after which the comparators 59 and 60 will cause the motor tobe energized to an extent necessary to cause the machine 10 to movesynchronously with the truck 13 as the truck 13 coasts to a stop.

The teach mode of operation is included in the control system to permitthe machine 10 to be manually controlled in its movement to a variablenumber of discreet positions relative to the workpieces 11 and 12 towhich the machine 10 can be later caused to move in automatic play-backmode. The operator's control module 32 is provided with a suitableswitch which will cause the system to operate in the automatic or teachmode and jog switches which, when operated, will energize the motor 26to jog machine 10 in either a fast or slow jogging speed. The teach modeof operation may be initiated by activating the teach and jog switchesin the control module 32. When the teach and jog switches are activated,the machine 10 will move to a desired position on the workpieces 1 1 and12 and the jog-hold circuit will operate in a manner which will be laterdescribed. During the movement of the machine 10 in the jogging mode,the coarse and fine command signals will be preset to correspond to thecoarse and fine feedback signals. When the machine 10 is in its desiredposition, and a suitable second switch within the control module 32 isactivated, the information which is stored within the coarse and finecounters 38 and 39 will be transferred into one bank of the memory 31.When the machine 10 is again jogged to a new position, the coarse andfine command signals again will be preset to correspond to the coarseand fine feedback signals so that the information which corresponds tothe new position may be transferred out of the command counters 38 and39 into the next sequenced bank of the memory 31. The movement of themachine 10 to any number of desired locations is repeated until thedesired number of spot weld locations are recorded in the memory 31.

When the jog switches are operated in the control module 32, the joghold circuit 34 will supply a suitable input to the switch module 61which will cause the drive motor 26 to rotate in either the forward orreverse direction at either a fast or slow speed, depending upon theactuation of the jog switches. The circuitry within the jog-hold module34 is arranged so that the rotation of the motor 26 progressivelyincreases to the selected jog speed when the jog switch is initiallyactuated and abruptly reduced when the jog switch is deactivated to aidin the accurate positioning of the electrodes 29 on workpieces l1 and12.

The circuits are shown in the drawings includes a plurality of solidstate logic units designated as NANDS, ANDS, NORS and JK type flipflops, all of which are well known to those skilled in the art, andprovide outputs in response to inputs as follows. A NAND provides aBoolean logic operation which yields a logic "0 output when all of itslogic input signals are logic 1" and a logic l output when any of itslogic input signals are logic 0. An AND provides a Boolean logicoperation which yields a logic l output when all its logic input signalsare logic l and a logic 0" output when any of its logic input signalsare logic 0." A NOR provides a Boolean logic operation which yields alogic l output when all of its logic input signals are logic 0" and alogic 0 output when any of its logic input signals are logic 1". A flipflop is a circuit that has two stable states and the capability ofchanging from one state to another with the application of a controlsignal and remaining in that state after removal of the signals. A JKflip flop is a flip flop having two inputs designated as J and K and atoggle designated as T which, upon a logic l to "0 change at its toggleT with a logic l on its .l input and a logic 0" on the K input, will setthe flip flop in the ON state and with a logic 0" on its J input and alogic 1 on the K input will set the flip flop in its OFF state. The JKflip flops as used herein also include a set input designated by aletter S which is not controlled by the signals appearing at the toggleT and will switch the flip flop to its ON state in response to a logic"0" signal at its set input S. A JK flip flop, when in the ON state,will supply a l at its E output and a "0" at its E output. When in theOFF state, a JK flip flop will supply a "0" at its E output and a 1 atits E output.

The coarse comparator circuit, shown in FIG. 2 and designated as 59 inFIG. 1, includes a coarse command flip flop CC, :1 feedback flip flopFB, a reset flip flop RS, a flip flop FWD designated as a forward flipflop, a flip flop REV designated as a reverse flip flop, a flip flop SSdesignated as the single shot flip flop, NANDS N1-N10, ANDS A1-A2, and aNOR 01. The coarse comparator circuit receives input signals from thecoarse command counter 38, the resolver 46 and the timing module 42,illustrated in FIG. 1, as are typically illustrated by the curves inFIG. 3. The coarse command counter provides the coarse command signalCC, the resolver 46 provides the coarse feedback siglal CFB and thetiming module 42 provides the signals 500 KHZ, REF and lMHZ. The forwardFWD and reverse REV flip flops have their outputs E and E connected tosupply inputs to ANDS A3-A6 which in turn provide inputs to a pair ofNORS 02 and 03.

The fine comparator circuit includes a flip flop FFWD which isdesignated as the fine forward flip flop, a flip flop FREV which isdesignated as the fine reverse flip flop, a flip flop FRS which acts asa fine reset flip flop, and NANDS which are designated as N1 l-N20. Thefine comparator circuit receives inputs from the fine command counter39, the resolver 47 and the timing module 42 shown in FIG. 1. The finecommand counter provides the fine command signal FC, the resolver 47provides the fine feedback signal FFB and the module 42 provides thesignals 500 KHZ and lMHZ. The signals FWP and REP are synchronized withthe fine command signal FC.

COARSE COMPARATOR CIRCUIT The NAND N7 has an input 1 connected to thesignal source REF and an input 2 connected to an output E of the flipflop RS. The flip flop RS is turned ON by a input from the 500 KHZsignal on its input S. in its ON state, the flip flop RS supplies a "1"signal at its output E. The source REF supplies a "0 signal pulse thathas a 500 nanosecond duration at a rate of 500 cycles per second. Thusevery 500 cycles the output of the NAND N7 switches to provide a 500nanosecond 0" to 1" signal pulse which is inverted by a NAND N8 andsupplied as a 1" to "0" input to the inputs S of the flip flop CC andthe flip flop FB respectively, so that flip flops CC and F3 are turnedON and respectively supply a 1" signal at their outputs E and a 0 signalat their outputs E. The flip flop CC has its toggle T connected toreceive a coarse command input signal CC and is switched to an OFF stateupon a l to 0" change in the signal CC. Similarly, the flip flop FB hasits toggle connected to receive the coarse feedback signal CFB and isswitched to an OFF state upon a 1 to 0 change in the signal CFB Thedifference in time of occurrence of a l to "0 signal change of thecoarse command signal CC and the coarse feedback signal CFB will providean error signal which is indicative of both the direction and thedistance which the coarse feedback resolver 46 must be rotated to reducethe error signal.

if the machine 10 is positioned so that the coarse feedback signal CFBchanges from 1 to "0" prior to a 1 to 0 change in the coarse commandsignal CC, the control will operate to rotate the resolver 46 in adirection to reduce the error signal which, for purposes of description,is designated as a reverse direction REV. Similarly, if the coarsecommand signal CC changes from 1 to 0" prior to a change of 1" to 0 ofthe coarse feedback signal CFB, the control will operate to reduce theerror signal and drive the resolver 46 in a forward direction FWD. inFIG. 3, the

curves indicate the signals appearing at the inputs and outputs of thedesignated solid state components relative to a train of 500 nanosecond0 pulses on a 500 cycles per second reference wave REF, when the controlis programmed so the coarse feedback signal CFB changes from 1" to 0"prior to a change of l to 0 of the coarse command signal CC.

The l to 0 signal change of the coarse feedback signal CFB to the toggleT of the flip flop FB causes the flip flop FB to switch OFF and a 1signal to appear at its output E and a 0 signal at its output E. The lsignal at output E of the flip flop F8 is supplied to an input 2 of theNAND N3, an input 1 of the NAND N5 and an input 3 of the AND A2. The 0"signal at output E of the flip flop F3 is supplied to the J input of theflip flop REV, an input 2 of the AND A1, and an input 2 of the NAND N1.The NAND N3 tlnrough its input 1 also receives an input of 1" from theoutput E of the flip flop CC which remains in its ON state because thecoarse command signal CC on its toggle T has not changed from l" to 0".Thus as both inputs 1 and 2 of the NAND N3 are l," the output of theNAND N3 switches to 0. The 0" output of the NAND N3 is inverted by aNAND N4 and is supplied as a l to the K input of the flip flop REV tocondition the flip flop REV to switch to an OFF state upon the receiptof a l to 0 signal change at its toggle T input. The AND A2 alsoreceives a 1" signal at its input 2 from the flip flop RS output E and a"1 signal at its input 1 from the output E of the flip flop CC. As allof the inputs to the AND A2 are now l it switches its output to supply a1" input to the NOR 01 which switches its output from 1" to0."

The output ofthe NOR 01 is supplied as a l to 0" input signal change tothe toggle T and the K input of the flip flop SS. The flip flop SS, inresponse to the l to 0" output signal change of the NOR 01, switches toan OFF state so that a "0" signal appears at its output E and a l signalappears at its output E. The l" to 0" signal change at the output E ofthe flip flop SS is inverted by the NAND N9 and supplied as a 0 to lsignal input change to the toggles T of the flip flops FWD and REV.

During the interval when the flip flop SS is switched ON and its outputE provides a 0 signal, the NAND N10 supplies a 1" signal to the input Sof the flip flop SS so that the flip flop SS is conditioned to switch toan OFF state upon the receipt of a 1" to 0" input signal change at itstoggle T and its input K. The switching of the flip flop SS to an OFFstate causes the signal at its output E to change from 0" to 1". This "0to l signal change is delayed in its transmission to the input of theNAND N10 by a capacitor C1 and a resistor R1 so that the NAND N10continues to supply a l signaltotheinputSoftheflipflopSSaftertheflipflopSShas switched to an OFFstate. After a fixed time delay, as detemrined by the RC constants ofthe resistor R1 and the capacitor C1, the charge on the capacitor C1increases to a value which causes the NAND N10 to switch and supply a"0" input signal to the input S of the flip flop SS. The 0" input signalto the input S of the flip flop SS causes the flip flop SS to switch toan ON state and the output of the NAND N9 to switch from "1 to "0". Theoutput of the NAND N9 is connected to the toggles T of the flip flopsFWD and REV.

Thus if the coarse command signal CC has not changed from 1" to prior tothe "l to 0 signal change from the NAND N9, the flip flop FWD willremain ON and the flip flop REV will switch to an OFF state because ofthe "1 input sigrnal at its K input and supply a l signal at its outputE and a "0" signal at its output E.

As shown in FIG. 3, subsequently to the switching OFF of the flip flopREV and prior to the receipt of the signal change from the signal sourceREF, the coarse command signal CC changes from 1" to 0.

The l to 0" change of the coarse command signal CC to the toggle T ofthe flip flop CC causes the flip flop CC to switch OFF so that a 1"signal appears at its output E and a 0" sigrnal at its output E. The lsigrnal at the output E of the flip flop CC is supplied to the input 2of the NAND N which also receives a l input from the flip flop FB at itsinput 1 so that the NAND N5 is conditioned to switch when the 500 KHZsignal at its input 3 switches to 1. When all of the inputs 1,2 and 3 ofthe NAND N5 are 1, "its output switches to 0. The 0 output of the NANDN5 is inverted by the NAND N6 and supplied as a 1" to the K input of theflip flop RS which switches to an OFF state upon the receipt of asubsequent l to "0 signal change to its toggle T in the lMl-IZ signal.The flip flop RS when in an OFF state switches the flip flops CC and FBto their ON states and supplies a 0" signal to the input 2 of the AND 2which causes the output of the AND A2 to switch from "1" to 0". The 0"output of the AND A2 causes the output of the NOR 01 and the input tothe toggle T of the flip flop SS to change from 0 to l to condition theflip flop SS for switching from its'ON to its OFF state when the signalat its toggle T again switches from 1" to 0 as previously described. TheI from the 500 KHZ signal, which caused the NAND N5 to switch and supplya 0" output sigrnal, is also supplied to the input S of the flip flopRS. Therefore when the 500 KHZ sigrnal switches from 1" to 0 subsequentto the switching of the NAND N5, the flip flop RS will switch to its ONstate.

Summarizing the foregoing, the switching of the flip flop F8 in responseto the I to 0 change in the coarse feedback signal CFB causes a l to besupplied to the K input of the flip flop REV and a "l" to 0" signalchange to be supplied to the toggle T of the flip flop SS. The flip flopSS, resistor R1, capacitor C1 and the NAND N10 function as a single shotcircuit and after a fixed time delay provide a "1" to 0" signal changeto he toggles T of the flip flops FWD and REV. If the time delayprovided by the single shot circuit is less than the time interval ofthe error signal, e.g., the interval between the 1" to 0 change in thecoarse feedback signal CFB and the l to 0" change in the coarse commandsignal CC, the 1" to 0 signal change to the toggle T of the flip flopFWD will not change the ON state of the flip flop FWD because of thecontinuing 0 that is supplied by the output E of the flip flop CC to theinput K of the flip flop FWO. The 1" to 0" signal change to the toggle Tof the flip flop REV however causes the flip flop REV to switch OFFbecause of the "1" input to its K input. The flip flop REV when OFFsupplies a 0" at its output E and a l at its output E and remains OFF aslong as the duration of the error signal is greater than the fixed timedelay provided by the single shot circuit.

The ANDS A3-A6 and the NORS 02 and 03 function as the switch 61 in FIG.1 as follows. The outputs E of the respective flip flops FWD and REV arerespectively connected to the inputs 1 of ANDS A3 and A5. The output Eof the flip flop FWD is connected to an input 2 of an AND A4 and aninput 1 of an AND A6. The output E of the flip flop REV is connected toan input 1 ofan AND A4 and an input 2 ofan AND A6. The ANDS A3 and A4have their outputs connected to the inputs 1 and 2 of a NOR 02 which hasits output connected through a digital to analog converter in thedeceleration module 62 in FIG. 1 to control the energization of a motor26 in a manner which will drive the position resolvers 44 and 45 in theforward direction. Similarly, the ANDS A5 and A6 have their outputsconnected to the inputs 1 and 2 of a NOR 03 which has its outputconnected through the deceleration module 62 to control the energizationof a motor 26 in a manner which will drive the position resolvers 44 and45 in a reverse direction. When both flip flops FWD and REV are ON, the1" signals appearing at their respective outputs B will appear as a "1signal at the inputs of the respective ANDS A4 and A6 so the ANDS A4 andA6 are respectively controlled by signals appearing at their inputs 3during fine positioning, as will be later described. Further, when bothflip flops FWD and REV are ON, the 0" signals appearing at theirrespective output E will cause the ANDS A3 and A5 to have 0" outputswhich permit the NORs 02 and 03 to be controlled by the outputs of theANDS A4 and A6.

The flip flop REV, when in an OFF state, supplies a 0" signal at itsoutput E and a l signal at its output E. The 0" signal at the output Ethereby blocks the switching of the ANDS A4 and A6 in response to thesignals from the fine positioning control, as will be later described.The 1" signal from the output E of the flip flop REV is supplied to aninput 1 of the AND AS which also receives a signal at its input 2 fromthe sigrnal source REP. The source REP supplies a signal that is 1"during 20 percent of each cycle of the 500 cycle/sec reference wave and"0 during the remainder of each cycle. Thus the NOR 03 will have a "0output for 20 percent of the time and energize the motor 26 to drive themotor 26 in the reverse direction to reduce the time duration of theerror signal.

FINE COMPARATOR CIRCUIT The solid state logic units in the finecomparator circuit will exist in the following states when the finecomparator circuit 60 is reset. The flip flop FFWD, the flip flop FREVand the flip flop FRS will be ON and provide a logic l at theirrespective E terminals and a logic 0" at their E terminals. The finecommand signal FC and the fine feedback signal FFB will each provide alogic 1 signal to the fine comparator circuit 60. The l signal from thefine command signal FC is supplied to the toggle T of the flip flop FFWDand causes the NAND N15 to have a 0 output which is inverted by the NANDN16 and supplied as a l" to the K input of the flip flop FREV. The logic"1 from the flne feedback signal FFB, which is supplied to the toggle Tof the flip flop FREV, causes the NAND N19 to have a 0 output which isinverted by the NAND N20 and supplied as a 1" to the K input of the flipflop FWD. The 0 output at the E output of the flip flop FFWD is suppliedto the input 2 of the NAND N11 and to the l input of the NAND N17 sothat the NANDS N11 and N17 will have a continuing 1 output. The outputat the E output of the flip flop FREV is supplied to an input 3 of theNAND N17 and an input 2 of the NAND N13 so that the NANDS N13 and N17provide a continuing 1" output. The continuing 1" outputs from the NANDSN11 and N13 are inverted by the NANDS N12 and N14 respectively andsupplied to the inputs 3 of the ANDS A4 and A6 respectively, so that theNORS 02 and 03 have a continuing "1 output. The output E of the flipflop FRS is supplied as a 1" to the inputs S of the flip flop FFWD andthe flip flop FREV. During the operation of the fine comparator circuit60, the ANDS A3 and A supply a continuous 1" to the inputs 1 of the NORS02 and 03 respectively.

If the control is programmed so that the fine feedback signal FFBchanges from 1 to 0 prior to a change from "1 to 0 in the fine commandsignal PC, the control will operate to rotate the fine feedback resolverin a direction to reduce the error signal which, for purposes ofdescription, is designated as the reverse direction. Similarly, if thesignal from the fine command signal FC changes from 1 to 0 prior to achange of "1" to 0 in the fine feedback signal FFB, the control willoperate to reduce the error signal and drive the fine feedback resolverin a forward direction. In FIG. 3 the curves indicate the signalsappearing at the inputs and outputs from the sources indicated and ofthe flip flops FWD and REV. Thus the output of the AND A6 switches to a1" which causes the NOR 03 to supply a 0 signal to the decelerationmodule 62 which will control the energization of a motor 26 in a mannerwhich will drive the position resolvers 44 and 45 in a reverse directionto reduce the error signal. As shown in FIG. 3, subsequent to the changeof the signal from 0" to 1 of the source REP, the fine command signal FCswitches from 1 to 0". The 1" to 0" change of the fine command signalFC, which is supplied to the toggle T of the flip flop FFWD, causes theflip flop FFWD to switch so that a 1 signal appears at its output E anda 0 signal at its output E.

The 1" to 0 change in the fine command signal FC also causes the NAND Nto supply a 1 to the input 1 of the NAND N16. However, the NAND N16continues to supply a 1" to the K input of the flip flop FREV as theNAND N16 now receives a 0" at its input 2 from the E output of the flipflop FFWD. The 1 at the output E of the flip flop FFWD is supplied to aninput 1 of the NAND N17 and an input 2 of the NAND N11 so that the NANDN17 now receives a "1" at each of its inputs 1 and 3 and is conditionedto be switched by the 500 KHZ signals. The 500 KHZ signal is supplied toboth the input 2 of the NAND N17 and the input S of the flip flop FRS.Thus during the half cycle when the 500 KHZ signal is 1," the input 8 ofthe flip flop FRS will be 1" and the output of the the designated solidcomponents when the machine 10 NAND N17 will be 0." The NAND N18 invertsthe is positioned so that the fine feedback signal FFB changes from 1 to0 prior to a change of 1" to 0" of the fine command signal FC. Thecontinuing l fine command signal through the NANDS N15 and N16 causes a1 signal input to be present at the K input of the flip flop FREV sothat the change of l to 0 in the fine feedback signal FFB, at the toggleT of the flip flop FREV, causes the flip flop FREV to switch OFF andsupply a 0" signal at its E output and a 1 signal at its E output.

The l to 0" change of the signal from the fine feedback signal FFB alsocauses the NAND N19 to supply a 1 to an input 1 of the NAND N20.However, the NAND N20 continues to supply a 1 to the K input of the flipflop FFWD as the NAND N20 now receives a 0 at its input 2 from the Eoutput of the flip flop FREV. The l at the output E of the flip flopFREV is supplied to an input 3 of the NAND N17 and an input 2 of theNAND N13. The output of the NAND N17 does not switch in response to the1" at its input 3 because it continues to receive a O at its input 1from the output E of the flip flop FFWD so that the flip flop FRSremains in its ON state. The 1" to the input of the NAND N13 permits thestate of the NAND N13 to be controlled by the signals from the sourceREP, which, as shown in FIG. 3, switches from a 0" to 1 72 prior to theswitching of the signal from the fine command signal PC from "1 to 0 sothat the signal from the source REP is "1 during 20 percent of eachcycle of the fine command signal FC. Thus 72 prior to the signal changein the fine command signal FC, the NAND N13 has a l on both of itsinputs 1 and 2 and thereby supplies a 0 input to the NAND N14 which inresponse thereto supplies a 1 to the input 3 of the AND A6. Aspreviously described. the AND A6 also receives a 1" at its inputs 1 and2 from the E outputs 0 output of the NAND N17 and supplies a 1 to the Kinput of the flip flop FRS which switches to an OFF state when thesignal at its toggle T from the 1 MHZ signal switches from 1" to 0. Theswitching to the ON state of the flip flop FRS causes the signal at itsE output to change from l to 0" and is supplied to the input S of boththe flip flops FFWD and FREV. The flip flops FFWD and FREV in responseto the 0 signals at their inputs S switch to an ON state andrespectively supply a 1 to the inputs 2 of the NANDS N16 and N20 so thatthe NANDS N16 and N20 now supply a 0 to the K inputs of the flip flopsFFWD and FREV. The flip flops FFWD and FREV when in the ON state alsosupply a 0 to the inputs 1 and 3 of the NAND N17 which in responsethereto through NAND N18 supplies a 0 to the input K of the flip flopFRS which causes the flip flop FRS to remain in its ON state after it isturned ON by a 0" pulse at its input S from the 500 KHZ signal on thesubsequent change of the 1 MHZ signal at its toggle T. Thus the flipflops FFWD, FRS, and FREV are all in the ON state so that a subsequentchange in the fine feedback signal FFB and the fine command signals from0" to 1 will cause the NANDS N20 and N16 to respectively supply a 1" tothe inputs K of the flip flops FFWD and FREV and restore the circuit toits reset state as previously described.

ln view of the foregoing, it is obvious that if the machine 10 ispositioned so that the coarse command signal CC changes from 1 to 0prior to a 1" to 0" change in the coarse feedback signal CFB, thecontrol will operate to rotate the resolvers 44 and 45 in a direction toreduce the error signal which, for purposes of description, isdesignated as the forward direction FWD, in a manner which may besummarized as follows. The flip flop CC will switch OFF in response tothe 1" to change in the coarse command signal CC and cause a "1 to besupplied to the K input of the flip flop FWD and a l to 0 signal changeto be applied to the toggle of the flip flop SS. Tlne flip flop SS,resistor R1, capacitor C1 and the NAND N function as a single shotcircuit and after a fixed time delay pro vide a l to 0 signal change tothe toggles T of the flip flops FWD and REV. If the time delay providedby the single shot circuit is less than the time delay interval of theerror signal, e.g., the interval between l to 0 change of the coarsecommand signal and the l to 0 change in the coarse feedback signal CFB,the l to 0 change to the toggle of the flip flop REV will not change theON state of the flip flop REV because of the continuing 0 that isapplied by the output E of the flip flop F8 to the input K ofthe flipflop REV. The l to 0 signal change to the toggle of the flip flop FWDhowever causes the flip flop FWD to switch OFF because of the 1" inputto its K input. The flip flop FWD when OFF supplies a 0" at its output Eand a l at its output E and remains OFF as long as the duration of theerror signal is greater than the fixed time delay provided by the singleshot circuit.

The flip flop FWD when in the OFF state, supplies a 0 signal at itsoutput E and a 1" signal at its output E. The 0 signal at the output Ethereby blocks the switching of the ANDS A4 and A6 in response to thesignals from the fine positioning control. The "1 signal at the output Eof the flip flop FWD is supplied to the 1 input of the AND A3 which alsoreceives a signal at its input 2 from the signal source FWP. The sourceFWP supplies a signal that is 1" during 20 percent of each cycle of the500 cycle reference wave after the coarse command signal CC changes froml to 0, and 0" during the remainder of the cycle. Thus the NOR 02 willhave a 0 output for 20 percent of the time and energize the motor 26 todrive the motor 26 at a constant speed in the forward direction toreduce the time duration of the error signal.

If the control is programmed so that the signal from the fine commandsignal FC changes from 1" to "0 prior to a change of "1 to 0" in thefine feedback signal FFB, the control will operate to reduce the errorsignal and drive the fine feedback resolver in a forward direction.

The 1" to 0" change of the sigrnal from the fine command signal FC alsocauses the NAND N to supply a 1 to an input 1 of the NAND N16. However,the NAND N16 continues to supply a "1 to the K input of the flip flopFREV as the NAND N16 now receives a 0 at its input 2 from the E outputof the flip flop FFWD. The l at the output E of the flip flop FWVD issupplied to an input 1 of the NAND N17 and an input 2 of the NAND N1 1.The output of the NAND N17 does not switch in response to the l at itsinput 1 because it continues to receive a 0 at its input 3 from theoutput E of the flip flop FREV so that the flip flop FRS remains in itsON state. The 1" to the input of the NAND N11 permits the state of theNAND N11 to be controlled by the signals from the source FWP whichexists as a 1" for 72 after the fine command signal FC switches from 1"to 0" so that the signal from the source FWP is l during 20 percent ofeach cycle. Thus during an interval of 72 after the fine command signalhas changed to "0", the NAND N11 has a l on all of its inputs andthereby supplies a "1 to the input 3 of the AND A4. As previouslydescribed, the AND A4 also receives a l at its inputs 1 and 2 from the Eoutputs of the flip flops FWD and REV. Thus the output of the AND A4switches to a 1" which causes the NOR 02 to supply a 0" signal to thedeceleration circuit 62 which will control the energization of a motor26 in a manner which will drive the position resolver 45 in a forwarddirection to reduce the error signal. As shown in FIG. 3, subsequent tothe change of the signal from 1 to 0 of the source FWP, the finefeedback signal FFB switches from 1" to 0. The l to 0" change of thefine feedback signal FFB, which is supplied to the toggle T of the flipflop FREV, causes the flip flop FREV to switch so that a l signalappears at its output E and a 0 sigrnal at its output E.

The 1" to 0" change in the fine feedback signal FFB also causes the NANDN19 to supply a l to the input 1 of the NAND N20. However, the NAND N20continues to supply a l to the K input of the flip flop FFWD as the NANDN20 now receives a "0 at its input 2 from the E output of the flip flopFREV. The l at the output E of the flip flop FREV is supplied to aninput 3 of the NAND N17 and an input 2 of the NAND N13 so that the NANDN17 now receives a l at each of its inputs 1 and 3 and is conditioned tobe switched by the 500 KHZ signals. The 500 KHZ signal is supplied toboth the input 2 of the NAND N17 and the input S of the flip flop FRS.Thus during the half cycle when the 500 KHZ signal is l, the input S ofthe flip flop FRS will be 1" and the output of the NAND.N17 will be 0.The NAND N18 inverts the 0 output of the NAND N17 and supplies a 1" tothe K input of the flip flop FRS which switches to an OFF state when thesignal at its toggle T from the l MHZ signal switches from 1 to 0. Theswitching to the OFF state of the flip flop FRS causes the signal at itsE output to change from l to 0 and is supplied to the input S of boththe flip flops FFWD and FREV. The flip flops FFWD and FREV in responseto the "0" signals at their inputs S switch to an ON state andrespectively supply a l to the inputs 2 of the NANDS N16 and N20 so thatthe NANDS N16 and N20 now supply a 0 to the K inputs of the flip flopsFFWD and FREV. The flip flops FFWD and FREV when in the ON state alsosupply a 0" to the inputs 1 and 3 of the NAND N17 which in responsethereto through NAND N18 supplies a 0" to the input K of tlne flip flopFRS which causes the flip flop FRS to remain in its ON state after it isturned ON by a 0 pulse at its input S from the 500 KHZ signal on thesubsequent change of the 1" to 0 of the l MHZ signal at its toggle T.Thus the flip flops FFWD, FRS, and FREV are all in the reset state.Subsequent to the resetting of the flip flops FFWD, FRS and FREV, thefine command signal FC and the fine feedback signal FFB will change from"0 to "1 and cause the NANDS N20 and N16 to respectively supply a1"totheirnputsKofthe flipflopsFFWDand FREV so as to restore the circuit toits reset state, as previously described.

Thus when the interval between the occurrence of the coarse command andfeedback signals is greater than the time interval as dictated by thesingle shot circuit that includes the flip flop SS, the motor 26 will beenergized with constant current to operate either in the forward or thereverse directions because of the 20 percent N time signal pulsesprovided by the sources FWP and REP. The cross-over at which the controlof the energization of the motor 26 is transferred from a control by thecoarse feedback signal to the fine feedback signal occurs when the timeinterval between the coarse feedback and command signals is less thanthe time interval as dictated by the switching of the single shotcircuit, including the flip flop SS. If the l to "0" signal changes inthe coarse feedback and coarse command signals CFB and CC occur beforethe single shot circuit, including the flip flop SS, times out, a 0"will be present at the E outputs of the flip flops CC and PB before thesignals at the toggles T of the flip flop FWD and REV changes from 1 to0" in response to the change in the output of the NAND N10, aspreviously described. The 0" at the E output of the flip flops CC and FErespectively will cause the K inputs of the flip flops REV and FWDrespectively to be 0 when the signal input to the respective toggleschanges from 1" to "0" so that neither of the flip flops FWD or REV willswitch OFF to cause the motor to be energized.

The flip flops FWD and REV, when in the ON state, will permit the ANDSA4 and A6 to be controlled by the signals in the fine comparatorcircuit. The crossover from the control in response to the coarsefeedback signal to the fine feedback signal is made to occur when thelinear axis is approximately 5 inches from the desired position, orwhere the coarse error is equivalent to 12 coarse counts by the intervalprovided by the timing circuit including the flip flop SS. Duringpositioning in response to the coarse error signal, the ANDS A3 or A5will cause the deceleration module 62 to be supplied with a signal thatis ON 20 percent of the time and OFF 80 percent of the time, regardlessof the magnitude of the position error. When the control is switched torespond to the fine feedback signal, the sources FWP and REP will causethe ANDS A4 or A6 to supply the deceleration module 62 with a signalthat is on 20 percent of the time and OFF 80 percent of the time. Thusthe energization of the motor will not change during cross-over frompositioning in response to the coarse error signal to positioning inresponse to the fine error signal. When the fine error signal becomesless than 200 counts, the deceleration module 62 will cause theenergization of the motor 26 to be progressively decreased in responseto a progressively decreasing fine error signal as the machine movesinto its preprogrammed position relative to the workpieces II and 12.

The reference signal REF appears as a 500 nanosecond pulse which isgenerated by the $00 I-IZ voltage wave as the polarity of the voltagechanges from positive to negative. The signal REF is used to reset thecounters 38 and 39. The 500 HZ reference voltage provides the inputs tothe resolvers 44 and 45 and the resolvers 44-47 are adjusted to havetheir outputs in phase with the coarse and fine command signals when thepin and the machine 10 are at the end position and the coarse and finecommand counters 39 and 38 provide command signals of 500 Hz. Thus if aposition equivalent to a count less than 500 is required, i.e., 250, themachine 10 will tend to move upstream. However, other switchingcircuits, not shown, will prevent the machine 10 from moving upstreambeyond I-IOLD-JOG CIRCUIT Referring to FIGS. 1 and 4, the hold and jogcircuit in FIG. 4 provides the functions included in the hold-jog module34 and the switch module 61 and receives the l MHZ, the 500 KHZ and the500 HZ reference input signals from the timing module 42. The switchesH, J F JR and FJ shown in FIG. 2 are included in the control module 32.The holdjog circuit provides inputs F and R to the deceleration module62 and inputs CCR and FCR to the coarse and the flne comparators 59-60.The circuit shown in FIG. 4 includes NANDS N2l-N59, flip flops SS1-SS3,F1-F4, CCR and FCR, Schmitt triggers STl and ST2, a timing module T, anda jog speed module 68.

During standby conditions, the hold switch H, the jog forward switch JF,the jog reverse switch JR and the fast jog switch FJ are open, so thatthe NANDS N21, N37, N50, N56 and N43 respectively receive a "0 input andprovide a 1 output. The flip flop SS1 is in an 0N state and supplies a 1at its E output and a 0" at its E output. The 1" at the E output of theflip flop SS1 is supplied to an input of the NAND N22 which alsoreceives a 1" input at its other two inputs in a manner which will belater described, so that the NAND N22 provides a 0 input to the NAND N23and causes the NAND N23 to have a l output. The "1 output of the NANDN23 causes the NAND N24 to supply a "0 to the J input of the flip flop Fl and a 0" to the input of the NAND N25 so that the NAND N25 supplies al to the K input of the flip flop F l and the set input S of the flipflop F2. The flip flop F l in response to the inputs at its J and Kinputs supplies a 0" at its E output and a l at its E output. The 0 atthe E output of the flip flop F1 is supplied to the K inputs ofthe flipflops F3 and F4. The l at the E output of the flip flop F1 is suppliedto the K input of the flip flop F2 and as an input BC to the coarse andfine comparator circuits shown in FIG. 2. The l to the K input of theflip flop F2 causes the flip flop F2 to provide a "1 at its E outputwhich is supplied to the inputs of the NANDS N32 and N33.

During standby conditions, the previously set flip flops CCR and FCRhave a 1" at their respective E outputs which are respectively suppliedthrough the NANDS N28 and N31 to the counters 39 and 38. The flip flopsF3 and F4 in response to the 0" at their K inputs have a 0" at their Eoutputs. The "0" at the E output of the flip flop F3 causes the NAND N26to supply a l input to the NAND N27 so that the NAND N27 supplies a 0 tothe K input of the flip flop CCR. The 0 at the E output of the flip flopF4 causes the NAND N29 to supply a 1" input to the NAND N30 so that theNAND N30 supplies a 0" to the K input of the flip flop FCR. The flipflop F3 receives the coarse feedback signal CFB at its toggle input Tand the flip flop FCR receives the fine feedback signal FFB at itstoggle T input. The 500 HZ signal is connected through the NAND N59 tosupply inputs to the toggle inputs T of the flip flops F1 and F2. The500 KHZ source supplies an input through a NAND N58 to the set inputs Sof the flip flops CCR and FCR as well as an input 1 of the NANDS N26 andN29. The l MHZ source supplies an input through the NAND N57 to thetoggle inputs T of the flip flops CCR and FCR so that the respectiveflip flops CCR and FCR supply outputs as described.

The hold period is initiated by closing the hold switch H so that a l issupplied to the input of the NAND N21. The NAND N21 has an outputconnected to the toggle input T of the flip flop SS1 which, togetherwith the timing circuit T, is arranged to act as a single shotmultivibrator. The 1 to change to the input T of the flip flop SS1switches the flip flop SS1 so that a 0 appears at its E output, whichcauses the NAND N22 to switch, and provide a l output as input to theNAND N23. The l to 0" signal change from the NAND N21 to the input T ofthe flip flop SS1 also causes the flip flop SS1 to switch and supply a0" to 1 signal change at its E output, which change is delayed for 380milliseconds and supplied by the timing circuit T as a l to 0 change tothe set input S of the flip flop SS1. The 0" signal to the input S ofthe flip flop SS1 causes the flip flop SS1 to switch and again supply a1" at its output E and a 0 at its output E, so that for 380 millisecondsafter the hold switch H is closed, a 0" ap pears at the output E of theflip flop SS1. The 0" output of the NAND N23 is first inverted by theNAND N24 and supplied as a l to the J input of the flip flop F1 andagain inverted by the NAND N25 and supplied as a 0" to the K input ofthe flip flop F1 and the S input of the flip flop F2. Flip flops F1 andF2 have their toggle inputs T connected through the NAND N59 to receivethe 500 HZ signals so that at an appropriate l to 0" signal change attheir inputs T, the flip flops F1 and F2 switch so that the flip flop F1supplies a l at its E output and a 0 at its E output. The l at the Eoutput of the flip flop F1 is supplied to the inputs K of the flip flopsF3 and F4 so that the flip flops F3 and F4 are conditioned to beswitched upon a 1" to 0 change at their toggle T inputs. The "0" at theE input of the flip flop F1 is supplied to the K input of the flip flopF2 and as the signal BC to the comparators 59-60. The signal BC, whichis supplied to the set inputs S of the flip flops FWD and REV and theNANDS N and N19 in the comparator circuits shown in FIG. 2, prevents theswitching of the flip flops FWD, REV, FFWD and FREV to their OFF statesand thus prevents the circuits within the comparators 59-60 fromswitching in response to the command signals and feedback signals. Theflip flop F2 in response to the 0 at its S input supplies a 0 at its Eoutput which causes the NANDS N32 and N33 to have a 1 output, the NANDSN34 and N35 to have a "0" output and the NAND N36 to have a 1" output.The output of the NANDS N35 and N36 are respectively supplied to thereverse and forward inputs R and F of the deceleration module 62 which,in response thereto, internipts the energization of the motor 26 to thatthe motor 26 begins to coast to a stop. The motor 26 causes the rotationof the feedback resolvers 44 and 45. The resolvers 46 and 47 have theirrespective outputs connected to supply the toggle inputs T of the flipflops F3 and F4 with the coarse and the line feedback signals CFB andFFB so that when the respective feedback signals CFB and FFB change from1" to 0, the flip flops F3 and F4 switch 0N and provide a 1 at theirassociated E outputs. The 1" at the E outputs of the flip flops F3 andF4 is supplied as an input to the NANDS N26 and N29 respectively. TheNANDS N26 and N29 also receive an input through the NAND N58 from the500 KHZ pulse source so that when the output of the NAND N58 changesfrom 0" to l," the NANDS N26 and N29 respectively will provide 0 inputsto the NANDS N27 and N30 and cause the NANDS N27 and N30 to switch andprovide a 1" to the K inputs of the flip flops CCR and FCR. The 1 outputof the NAND N58, which caused the NANDS N27 and N30 to have l outputs isalso supplied as an input to the set inputs S of the flip-flops CCR andFCR so that the flip flops CCR and FCR are conditioned to switch andsupply a 0' at their associated E outputs upon a suitable 1 to 0 changefrom the IMHZ source through the NAND N57 at their associated inputs Twhich occurs 500 nanoseconds after the signal change at their set inputsS.

The 0 at the E outputs of the flip flops CCR and FCR, which arerespectively supplied to the set inputs S of the flip flops F3 and F4,causes the flip flops F3 and F4 to switch and again supply a 0 at theirassociated E outputs. The 0 at the E outputs of the flip flops F3 and F4is respectively supplied to the K inputs of the flip flops CCR and FCRthrough the associated NANDS N26-N30. Thus 500 nanoseconds after theflip flops CCR and FCR are switched to supply a "0" at their associatedE outputs, a signal change of 1" to "0 at the S input of the flip flopsCCR and FCR from the 500 KHZ source through the NAND N58 causes the flipflops CCR and FCR to switch and again supply a l at the associated Eoutputs. Thus as the motor M coasts to stop, the counters 38 and 39 willbe reset with a 0" pulse that has a 500 nanosecond duration each timethe coarse and the fine feedback signals CFB and FFB respectively changefrom 1" to 0," which occurs at a rate of 500 cycles per second orapproximately times during the 380 millisecond interval as determined bythe switching of the flip flop SS1.

As previously described, the single shot flip flop SS1 switches toprovide a l at its E output 380 milliseconds after the switch H isclosed. The "1 at the E output of the flip flop SS1 switches the NANDSN22-N25 so that the NAND N24 supplies a 0 to the J input of the flipflop F1 and the NAND N25 supplies a l to the input S of the flip-flop F2and a l" to the input K of the flip flop F1 so that the flip flops F1and F2 are conditioned to switch to their standby states upon thereceipt of the suitable "1 to "0" at their inputs T from the 500 HZsource through the NAND N59. When the flip flops F1 and F2 are in theirstandby states, the E output of the flip flop F1 is "0 and the E outputsof the flip flops F1 and F2 are l." The 0" at the E output of the flipflop F1, which is supplied to the K inputs of the flip flops F3 and F4,causes the flip flops F3 and F4 to remain in their OFF states so thattheir E outputs are a continuous "0" in spite of the fact that the flipflops F3 and F4 are receiving a "l" to 0" signal change at their toggleinputs T from the feedback signals CFB and FFB. The to 1 change at the Eoutput of the flip flop Fl, which is supplied to the input K of the flipflop F2, causes the flip flop F2 to switch to its standby state when thesignal at its toggle input T from the NAND N59 changes from 1 to 0. The1" at the E output of the flip flop F2 removes the blocking signal BC tothe comparators 59-60 so that the operation of the circuitry within thecomparators 59-60 is restored. The l signal at the E output of the flipflop F2, when the flip flop F2 is reset, permits the NANDS N32 and N33to have a 0" output, the NANDS N34 and N35 to have a 1 output and theNAND N36 to have a 0" output so that the outputs of the NANDS N35 andN36 are in their standby conditron.

The motor M may be caused to operate in a jogging mode either in theforward direction when the jog forward switch JF is closed, or in thereverse direction when the jog reverse switch JR is closed. Duringstandby conditions, that is, when both switches JF and JR are open, theforward and reverse jog circuits will be conditioned as follows. TheNAND N37 will have a 0" input and supply a l output to the NAND N38 andthe NAND N40. The NAND N38 is connected to the NAND N39 so that theNANDS N38 and N39 act as a NAND memory. The NAND N50 will have a "0input and therefore supply a l input to the NANDS N51 and N40. The NANDN51 is connected to the NAND N52 so that the NANDS N51 and N52 act as aNAND memory. The NAND N40, during standby, has a l on all of its outputsand supplies a 0 to a circuit within a jog speed module 68. The 0" inputto the module 68 causes the circuitry within the module 68 to supply a1" input to the NAND N41 through a solid state Schmitt trigger ST] and"0" input signal pulses to the NAN DS N42 and N43 through a solid stateSchmitt trigger ST2. The 1" input to the NAND N41 causes the NAND N41 tosupply a 0 to the inputs of the NANDS N39 and N52 which switches theNAND memories so that the NANDS N38 and N51 have a 0 output and theNANDS N39 and N52 have a l output. The 1" output of the NANDS N39 andN52 are respectively supplied to a pair of inputs of the NAND N22 in thehold circuit which permits the NAND N22 to be switched in response tothe 1" to "0" signal change from the E output of the flip flop SS1 whenthe switch H is closed, as previously described. The "0 outputs of theNANDS N38 and N51, which are respectively supplied as inputs to theNANDS N47 and N53, cause the NANDS N47 and N53 to have a 1 output. Theoutput of the NAND N47 is supplied to an input of the NAND N48 whichalso receives a 1 input from the NAND N52 so that the NAND N48 suppliesa 0" output which is inverted by the NAND N49 and supplied as a "1"input to the NAND N34. The "0 output of the NAND N51 causes the NAND N53to have a 1 output which is supplied as an input to the NAND N54. TheNAND N54 also receives a "1 at its other input from the NAND N39 so thatthe NAND N54 supplies a 0 input to the NAND N55 and causes the NAND N55to supply a 1" as an input to the NAND N35. The comparators 59-60 haveoutputs F and R respectively connected as inputs to the NANDS N32 andN33. When positioning is not required, the outputs F and R of thecomparators 59 and 60 are a continuous 1." Thus when positioning is notrequired and the job switches J F and JR are open, all of the inputs ofthe NANDS N32 and N33 will be l and the NANDS N32 and N33 will provide a0 output. hen the motor 26 is to be rotated in the forward direction,the signal at the F output of the comparators 59-60 will be pulsed to a0" and cause the NAND N32 to provide a 1 output pulse. Similarly, whenthe motor 26 is to be rotated in a reverse direction, the signal at theR output of the comparators 59-60 will be pulsed to 0 and cause the NANDN33 to provide a 1" output pulse. When the NAND N32 has a 0 output, theoutput of the NAND N34 will be l and the output of the NAND N36 0, whichis supplied to the F input of a deceleration module 62. When the NANDN33 has a 0 output, the NAND N35 will have a "1 output, which issupplied to the R input of the deceleration module 62. A switch in theoutput of the NAND N32 from the "0 to l will cause the output ofthe NANDN36 to switch from O to 1" and the deceleration module 62 to provide anoutput which will cause the motor 26 to operate in the forwarddirection. Similarly, a change in the output of the NAND N33 from 0" to"1" will cause the output of the NAND N35 to switch from 1" to 0" andthe deceleration module 62 to provide an output which will cause themotor 26 to operate in the reverse direction. However, the circuitrywithin the deceleration module 62 is arranged so that when the inputs tothe NANDS N32 and N33 are simultaneously 0", as occurs during the 380milliseconds when the switch H is closed, the deceleration module 62will not have an output which will cause the motor 26 to operate ineither the forward or the reverse directions. The output of the NANDSN42 and N43 are respectively connected to the toggle inputs T of theflip flops SS2 and SS3. The flip flops SS2 and SS3 have their E outputsconnected to supply an input to the NAND N46. The flip flop SS2 has itsE output connected through a time delay circuit consisting of anadjustable resistor R and a capacitor C to an input of the NAND N44which in turn has its output connected to the set input S of the flipflop SS2. The flip flop SS3 has its E output connected through a timedelay circuit consisting of an adjustable resistor R and capacitor C toan input of the NAND N45 which has its output connected to the set inputS of the flip flop SS3. When the flip flops SS2 and SS3 are set, theyrespectively supply a "1" at their E outputs and a "0" at their Eoutputs. The NAND N46 in response to the 1 at the E outputs of the flipflops SS2 and SS3 provides a 0 input to the NANDS N47 and N53 whichprevents the NANDS N47 and N53 from being switched when the outputs ofthe NANDS N38 and N51 become 1" as will be later described.

During intervals when the fast jog switch FJ is open, the NANDS N56 andN43 have a 0 input and respectively supply a 1 input to the NAND N42 andthe toggle input T of the flip flop SS3. The l input to the NAND N42from the NAND N56 permits the NAND N42 to be switched when the outputsignal pulses through the Schrnitt trigger ST2 change to "1." The 0"input to the NAND N43 prevents the NAND N43 from switching when theoutput pulses of the Schmitt trigger ST2 switches from 0" to 1."

1. A control system for positioning a machine at desired positions alonga workpiece while the workpiece is moving along a predetermined pathrelative to a datum position comprising: means for moving the machinealong a path relative to the datum position, means for moving theworkpiece along its path of movement relative to the datum position,means for electrically synchronizing and controlling the movement of themachine with respect to the movement of the workpiece, saidsynchronizing and movement controlling means including: an alternatingcurrent source providing a cyclic reference voltage wave having apredetermined phase, a first position responsive means including a firstsynchro resolver having a rotatable shaft, a pair of input windingswound in spaced quadrature and an output winding that provides a cyclicoutput voltage signal which varies in phase relative to thepredetermined phase with the angular position of the shaft when theinput windings are respectively energized from the alternating currentsource by equal magnitude alternating voltage inputs that are inquadrature, means providing a connection between the means for movingthe machine and the shaft of the first resolver for rotating the shaft360* when the machine is moved a predetermined distance from the datumposition along its path of movement, a second position responsive meansincluding a second synchro resolver having a rotatable shaft, a pair ofinput windings wound in spaced quadrature and an output winding thatprovides a cyclic output voltage signal which varies in phase relativeto the phase of the voltages across its input windings with the angularposition of the shaft when the input windings are respectively energizedby equal magnitude alterNating voltage inputs that are in quadrature,means providing a connection between the means for moving the workpieceand the shaft of the second resolver for rotating the shaft 360* whenthe workpiece if moved from the datum position along its path ofmovement a distance equal to the predetermined distance, means energizedby the cyclic output voltage signal of the first resolver for energizinga first of the pair of input windings of the second resolver with aninput voltage that is in phase with the cyclic output voltage of thefirst resolver and a second of the pair of input windings of the secondresolver with an input voltage that is in quadrature and equal inmagnitude to the voltage input to the first winding, means energized bythe alternating current source for energizing a first of the pair ofinput windings of the first resolver with an input voltage that is inphase with the reference voltage wave and a second of the pair of inputwindings of the first resolver with an input voltage that is inquadrature and equal in magnitude to the input voltage to the firstwinding, means energized by the cyclic output voltage signal of thesecond resolver for producing a feedback signal that appears as apredetermined voltage change which occurs at a predetermined instantduring each cycle of the cyclic voltage output signal of the secondresolver, means for producing a command signal that is incrementallyrepresentative by an amount dependent upon the displacement of a desiredposition of the machine from the datum position, said command signalproducing means including a counter energized by the reference voltagesource and a means including a memory for resetting and presetting thecounter at a predetermined point on the reference voltage wave so thecounter provides an output signal that appears as a predeterminedvoltage change that is incrementally displaced a predetermined number ofelectrical degrees from the predetermined point on the cyclic referencevoltage wave by an amount dependent upon the displacement of the desiredposition of the machine from the datum position, means for comparing thefeedback signal with the command signal during each cycle of thereference wave and providing an error signal of a magnitude dependentupon the difference in time of occurrence between the voltage change ofthe feedback signal and the command signal and direction indication thatis dependent upon the order of occurrence during each cycle of thereference wave of the voltage change of the feedback signal and thecommand signal, and means responsive to the error signal for causing themeans for moving the machine to move said machine in the directionindicated by the error signal at a rate determined by the magnitude ofthe error signal whereby the machine is moved from a first desiredposition to a second desired position along the workpiece while theworkpiece is moving in its path of movement relative to the datumposition.
 2. A control system for positioning a machine at desiredpositions along a workpiece while the workpiece is moving along apredetermined path relative to a datum position comprising: means formoving the machine along a path relative to the datum position, meansfor moving the workpiece along its path of movement relative to thedatum position, an alternating current source providing a cyclicreference voltage wave having a fixed phase, means for producing acommand signal that is incrementally representative by an amountdependent upon the displacement of a desired position of the machinefrom the datum position, said command signal producing means including acounter energized by the reference voltage wave and a means including amemory for resetting and presetting the counter at a predetermined pointon the reference voltage wave so the counter provides an output signalthat appears as a predetermined voltage change that is incrementallydisplaced a predetermined number of electrical degrees from thepredetermined point on the cyclic refErence voltage wave by an amountdependent upon the displacement of the desired position of the machinefrom the datum position, means including a fine position synchroresolver and a coarse position synchro resolver, with each resolverhaving a rotatable shaft, a pair of input windings wound in spacedquadrature and an output winding that provides a cyclic output voltagesignal which varies in phase relative to the predetermined phase withthe angular position of the shaft when the input windings arerespectively energized from the source by equal magnitude alternatingvoltage inputs that are in quadrature, means providing a connectionbetween the means for moving the machine and the shaft of the coarseresolver for rotating the shaft of the coarse resolver 360* when themachine is moved a predetermined distance from the datum position andthe shaft of the fine resolver for rotating the shaft of the fineresolver a fixed multiple of 360* when the machine is moved saidpredetermined distance, means including a fine feedback synchro resolverand a coarse feedback synchro resolver with each of said feedbackresolvers having a rotatable shaft, a pair of input windings wound inspaced quadrature and an output winding that provides a cyclic outputvoltage signal that varies in phase relative to the phase of thevoltages across its input windings when the input windings arerespectively energized by equal magnitude alternating voltage inputsthat are in quadrature, means providing a connection between the meansfor moving the workpiece and the shaft of the coarse feedback resolverfor rotating the shaft of the coarse feedback resolver 360* when theworkpiece is moved from the datum position along its path of movement adistance equal to the predetermined distance and the shaft of the finefeedback for rotating the shaft of the fine feedback resolver said fixedmultiple of 360* when the workpiece is moved said predetermineddistance, means energized by the cyclic output voltage signal of thecoarse resolver and means energized by the cyclic output voltage signalof the fine resolver for respectively energizing the associate pairs ofinput windings of the coarse feedback resolver and the fine feedbackresolver with input voltages, so that a first of the pair of inputwindings of the coarse feedback resolver is energized by a voltage thatis in phase with the output voltage of the coarse resolver, a second ofthe pair of input windings of the coarse feedback resolver is energizedby a voltage that is in quadrature and equal in magnitude to the voltageinput to the first winding of the coarse feedback resolver, a first ofthe pair of input windings of the fine feedback resolver is energized bya voltage that is in phase with the output voltage of the fine resolverand a second of the pair of input windings of the fine feedback resolveris energized by a voltage that is equal in magnitude and in quadratureto the voltage input to the first winding of the feedback resolver,means energized by the source for respectively energizing the associatedpairs of input windings of the coarse resolver and the fine resolverwith input voltages so that a first of the pairs of input windings ofthe coarse resolver and the fine resolver respectively are energizedwith an input voltage that is in phase with the fixed phase and a secondof the pair of input windings of the coarse resolver and the fineresolver respectively are energized by a voltage that is equal inmagnitude and in quadrature with the voltage input to its associatedfirst winding, means energized by the output signal from the coarsefeedback resolver and means energized by the output signal of the finefeedback resolver for respectively producing a coarse feedback signaland a fine feedback signal with said feedback signals appearing as apredetermined voltage change which occurs at a predetermined instantduring each cycle of the cyclic voltage output signal of its associatedresolver, means for rEspectively comparing the coarse feedback signaland the fine feedback signal with the command signal and providing acoarse error signal dependent upon the difference in time of occurrencebetween the voltage change of the coarse feedback signal and the commandsignal and a direction indication that is dependent upon the order ofoccurrence during each cycle of the reference voltage wave of thevoltage change of the coarse feedback signal and the command signalduring intervals when the time of an occurrence between the coarsefeedback signal and the command signal exceeds a predetermined timeinterval and providing a fine error signal having a magnitude dependentupon the difference in time of occurrence between the voltage change ofthe fine feedback signal and the command signal and a directionindication that is dependent upon the order of occurrence during eachcycle of the reference voltage wave of the voltage change of the finefeedback signal and the command signal when the time of occurrencebetween the coarse feedback signal and the command signal is shorterthan the predetermined interval, and means responsive to the coarseerror signal and the fine error signal for causing the means for movingthe machine to move the machine in the direction indicated by said errorsignals at a predetermined rate when the time of occurrence between thecoarse feedback and the command signal exceeds the predeterminedinterval and at a rate determined by the magnitude of the fine errorsignal when the time of occurrence between the coarse feedback signaland the command signal is shorter than the predetermined intervalwhereby the machine is moved from a first desired position to a seconddesired position along the workpiece while the workpiece is moving inits path of movement relative to the datum position.
 3. The controlsystem as recited in claim 1 including a selectively operable hold meansfor de-energizing the means for moving the machine from the firstposition to the second position as the workpiece is moved in its path,said hold means including a means when actuated for preventing thecounter from being reset and preset by the memory means and for causingthe counter to be reset and preset by the voltage change of the feedbacksignal during a brief interval after the hold means is initiallyactuated so that the counter provides an output signal that occur at thesame instant as the feedback signal after the brief interval.
 4. Thecontrol system as recited in claim 3 wherein the first positionresponsive means includes a first additional synchro resolver inaddition to the first resolver, said first additional resolver having arotatable shaft, a pair of input windings wound in spaced quadrature andan output winding that provides a cyclic output voltage signal whichvaries in phase relative to the predetermined phase with the angularposition of the shaft when the input windings are respectively energizedfrom the source by equal magnitude voltage inputs that are inquadrature, the means providing a connection between the means formoving the machine and the shaft of the first resolver also provides aconnection between means for moving the machine and tee shaft of thefirst additional resolver for rotating the shaft of the first additionalresolver a predetermined number of revolutions when the shaft of thefirst resolver is rotated 360*, the second position responsive meansincludes a second additional synchro resolver in addition to the secondresolver, said second additional resolver having a rotatable shaft, apair of output windings wound in spaced quadrature and an output windingthat provides a cyclic output voltage signal which varies in phaserelative to the phase of the voltages across its input windings with theangular position of the shaft when the input windings are respectivelyenergized by equal magnitude voltage inputs that are in quadrature, themeans providing a connection between the means for moving the workpieceand the shaft of the second resolver also provides a connection betweenthe means for moving the workpiece and the shaft of the secondadditional resolver for rotating the shaft of the second additionalresolver said predetermined number of revolutions when the shaft of thesecond resolver is rotated 360*, the control system includes a meansenergized by the cyclic output voltage signal of the first additionalresolver for energizing a first of the pair of input windings of thesecond additional resolver with an input voltage that is in phase withthe cyclic output voltage of the first additional resolver and a secondof the pair of input windings of the second additional resolver with aninput voltage that is in quadrature and equal in magnitude to thevoltage input to the first winding of the second additional resolver, ameans energized by the alternating current source for energizing a firstof the pair of input windings of the first additional resolver with aninput voltage that is in phase with the reference voltage wave and asecond of the pair of input windings of the first additional resolverwith an input voltage that is in quadrature and equal in magnitude tothe input voltage to the first winding of the first additional resolver,a means energized by the cyclic output voltage signal of the secondadditional resolver for producing a fine feedback signal that appears asa predetermined voltage change which occurs at a predetermined instantduring each cycle of the cyclic voltage output signal of the secondresolver, the means for comparing the feedback signal from the secondresolver with the command signal includes a means for comparing the finefeedback signal with the command signal during each cycle of thereference wave and providing said error signal when the difference intime of occurrence between the voltage change of the feedback signal andthe command signal is less than a predetermined value, and the holdmeans includes a means for causing the counter to be reset and preset bythe voltage change of the fine feedback signal during the brief intervalafter the hold means is initially actuated.
 5. The control system asrecited in claim 3 wherein the machine is moved along its path by a leadscrew and the means providing the connection between the first resolverand the first additional resolver is rotated by the lead screw.
 6. Thecontrol system as recited in claim 5 wherein the means providing aconnection between the means for moving the workpiece and the secondresolver and the second additional resolver includes a synchronizingchain which moves the workpiece relative to the datum position and ameans driven by the chain for rotating the shafts of the second resolverand the second additional resolver.
 7. The control system as recited inclaim 3 including a jog means for causing the machine to move relativeto the workpiece in a jogging mode and independently of the positiondictated by the command signal when the jog means is activated and ameans for causing the hold means to prevent the counter from being resetand preset by the memory means and for causing the counter to be resetand preset by the voltage change of the feedback signal and the finefeedback signal during periods when the jog means is actuated.
 8. Thecontrol system as recited in claim 2 wherein the means for moving themachine includes an electric motor, the means for comparing the coarseand the fine feedback signals respectively with the coarse and the finecommand signal has two outputs, the coarse error signal appears as atrain of constant width pulses appearing at a first of the two outputswhen the voltage change of the coarse feedback signal occurs prior tothe voltage change of the coarse command signal and the interval betweenthe voltage changes of the coarse feedback and coarse command signals isgreater than a predetermined interval, the coarse error signal appearsas a train of constant width pulses appearing at a second of the twooutputs when the voltage change of the coarse commAnd signal occursprior to the voltage change of the coarse feedback signal when theinterval between the changes of the coarse command and coarse feedbacksignals is greater than the predetermined interval, the fine errorsignal appears as a train of pulses appearing at the first output whenthe voltage change of the fine feedback signal occurs during thepredetermined interval prior to the voltage change of the fine commandsignal, the fine error signal appears as a train of pulses appearing atthe second output when the voltage change of the fine command signaloccurs during the predetermined interval prior to the voltage change ofthe fine feedback signal, the width of said fine error pulses at thefirst and the second outputs being equal to the interval between thechanges in the fine command and the fine feedback signals, and the meansresponsive to the coarse error signal and the fine error signalincludes: means responsive to the train of pulses at the first outputfor causing the motor to rotate in one direction at a constant speed inresponse to the constant width pulses and at a speed proportional to thewidth of the fine error pulses, and means responsive to the train ofpulses at the second output for causing the motor to rotate in adirection opposite said one direction at a constant speed in response tothe constant width pulses and at a speed proportional to the width ofthe fine error pulses.
 9. The control system as recited in claim 4wherein the means for moving the machine includes an electric motor, themeans for comparing the coarse and the fine feedback signalsrespectively with the coarse and the fine command signal has twooutputs, the coarse error signal appears as a train of constant widthpulses appearing at a first of the two outputs when the voltage changeof the coarse feedback signal occurs prior to the voltage change of thecoarse command signal and the interval between the voltage changes ofthe coarse feedback and coarse command signals is greater than apredetermined interval, the coarse error signal appears as a train ofconstant width pulses appearing at a second of the two outputs when thevoltage change of the coarse command signal occurs prior to the voltagechange of the coarse feedback signal when the interval between thechanges of the coarse command and coarse feedback signals is greaterthan the predetermined interval, the fine error signal appears as atrain of pulses appearing at the first output when the voltage change ofthe fine feedback signal occurs prior to the voltage change of the finecommand signal, the fine error signal appears as a train of pulsesappearing at the second output when the voltage change of the finecommand signal occurs prior to the voltage change of the fine feedbacksignal, the width of said fine error pulses at the first and the secondoutputs being equal to the interval between the changes in the finecommand and the fine feedback signals, and the means responsive to thecoarse error signal and the fine error signal includes: means responsiveto the train of pulses at the first output for causing the motor torotate in one direction at a constant speed in response to the constantwidth pulses and at a speed proportional to the width of the fine errorpulses, and means responsive to the train of pulses at the second outputfor causing the motor to rotate in a direction opposite said onedirection at a constant speed in response to the constant width pulsesand at a speed proportional to the width of the fine error pulses. 10.The control system as recited in claim 2 wherein the means for movingthe machine includes an electric motor, the means for comparing thecoarse and the fine feedback signals respectively with the coarse andthe fine command signal has two outputs, the coarse error signal appearsas a train of constant width pulses appearing at a first of the twooutputs when the voltage change of the coarse feedback signal occursprior to the voltage change of the coarse command signal and theinterval between the voltage changes of the coarse feedback and coarsecommand signals is greater than a predetermined interval, the coarseerror signal appears as a train of constant width pulses appearing at asecond of the two outputs when the voltage change of the coarse commandsignal occurs prior to the voltage change of the coarse feedback signalwhen the interval between the changes of the coarse command and coarsefeedback signals is greater than the predetermined interval, the fineerror signal appears as a train of pulses appearing at the first outputwhen the voltage change of the fine feedback signal occurs prior to thevoltage change of the fine command signal, the fine error signal appearsas a train of pulses appearing at the second output when the voltagechange of the fine command signal occurs prior to the voltage change ofthe fine feedback signal, the width of said fine error pulses at thefirst and the second outputs being equal to the interval between thechanges in the fine command and the fine feedback signals, the meansresponsive to the coarse error signal and the fine error signalincludes: means responsive to the train of pulses at the first outputfor causing the motor to rotate in one direction at a constant speed inresponse to the constant width pulses and at a speed proportional to thewidth of the fine error pulses, and means responsive to the train ofpulses at the second output for causing the motor to rotate in adirection opposite said one direction at a constant speed in response tothe constant width pulses and at a speed proportional to the width ofthe fine error pulses, and wherein the control system includes aselectively operable hold means for preventing the energization of themotor as the workpiece is moved in its path, said hold means including ameans when actuated for preventing the counter from being reset andpreset by the memory means and for causing the counter to be reset andpreset by the voltage change of the feedback signal during a briefinterval after the hold means is initially actuated so that the counterprovides an output signal that occurs at the same instant as thefeedback signal when the hold means is actuated and a jog means forcausing the machine to move relative to the workpiece in a jogging modeand independently of the position dictated by the command signal whenthe jog means is activated and a means for causing the hold means toprevent the counter from being reset and preset by the memory means andfor causing the counter to be reset and preset by the voltage change ofthe feedback signal and the fine feedback signal during periods when thejog means is actuated.
 11. The control system as recited in claim 3wherein the hold means includes a first flip flop having an outputproviding an input to the comparing means for preventing the comparingmeans from comparing the feedback signal with the command signal duringthe brief interval when the hold means is actuated, a second flip flophaving an output providing an input to the means for moving the machinefor preventing the machine moving means from responding to the errorsignal during the brief interval when the hold means is actuated, and athird flip flop and the means for preventing the counter from beingreset and preset by the memory means and for causing the counter to bereset and preset by the feedback signal includes an output of the thirdflip flop.
 12. The control system as recited in claim 14 including a jogmeans having output producing means which, when the jog means isenergized, will provide an input to the hold means which will cause thefirst, the second and the third flip flops to provide their respectiveoutputs to the comparing means, the means for moving the machine and themeans for causing the counter to be reset and preset by the feedbacksignal.
 13. The control system as recited in claim 15 wherein the meansfor moving the machine includes an electric motor and the jog meansincludes selectively operable means for seleCtively causing the motor torotate in either of two selected directions at either of two selectedspeeds when the jog means is energized.
 14. The control system asrecited in claim 16 wherein the jog means includes means for causing themotor to accelerate at a first predetermined rate when the jog means isenergized and to decelerate at a second predetermined rate when the jogmeans is de-energized.
 15. The control system as recited in claim 1wherein the means for moving the machine includes an electric motor andthe control system includes a jog means for causing the motor to rotatein either of two selected directions at either of two selected speedswhen the jog means is energized.
 16. The control system as recited inclaim 18 wherein the jog means includes means for causing the motor toaccelerate at a first predetermined rate when the jog means is energizedand to decelerate at a second predetermined rate when the jog means isde-energized.
 17. The control system as recited in claim 19 wherein themeans for causing the motor to accelerate at the first predeterminedrate and to decelerate at a second predetermined rate when the jog meansis respectively energized and de-energized includes: a first capacitor,means for increasing the level of a charge across the first capacitor atthe first predetermined rate to a predetermined level when the jog meansis initially energized, means for decreasing the level of the chargeacross the first capacitor from the predetermined level at the secondpredetermined rate after the jog means is de-energized, a secondcapacitor, means including a first transistor having a conductive levelcontrolled by the level of the charge on the first capacitor and havingelectrodes connected in a charging circuit for the second capacitor forcausing the rate at which the second capacitor is charged to becontrolled by the level of the charge across the first capacitor, meansfor producing pulses at a frequency controlled by the level of thecharge on the first capacitor, said pulse producing means including aprogrammable unijunction transistor having electrodes connected so theunijunction transistor is switched to a conductive state by the chargeon the second capacitor when the level of the charge across the secondcapacitor reaches a predetermined value and provides an output pulse andcauses the second capacitor to be discharged when the unijunctiontransistor is switched to its conductive state as the second capacitoris alternately charged by current flow through the first transistor anddischarged through the conducting unijunction transistor, meansincluding a second transistor having electrodes connected so theconductive level of the second transistor is controlled by theconductive level of the first transistor for providing an output signalchange when the conductive level of the first transistor causes thecharge on the second capacitor to equal the predetermined value, andtiming means having an input receiving the output pulses of the pulseproducing means and providing constant width output pulses at the samefrequency as the output pulses of the pulse producing means.
 18. Thecontrol system as recited in claim 1 wherein the error signal appears asa train of constant frequency pulses at each of two terminals with thepulses at a first of the two terminals appearing as a logic ''''1''''pulse which changes from a logic ''''0'''' which progressively decreasesfrom a constant width to zero as the machine moves in a first directiona predetermined distance to a desired position, and the pulses at asecond of the two terminals appearing as a logic ''''0'''' pulse whichchanges from a logic ''''1'''' and progressively decreases from aconstant width to zero as the machine moves in a second direction thatis opposite the first direction the predetermined distance to thedesired position, and the means for moving the machine in response tothe error signal includes an electric motor which wIll move the machinein the first direction when the motor rotates in a first direction andin the second direction when the motor rotates in a second directionthat is opposite the first direction, and a circuit for controlling thedirection of rotation and the speed of rotation of the motor in responseto the pulses at the first and the second terminals, said circuitcomprising: a capacitor means controlled by the train of pulses at thetwo terminals for maintaining the capacitor in a discharged state whenthe first and the second terminals are simultaneously ''''0'''' and''''1'''' respectively and when the first and the second terminals aresimultaneously ''''1'''' and ''''0'''' respectively and for causing thecapacitor to be charged in a first direction with a current flowing in afirst direction during periods when the first and the second terminalsare simultaneously ''''1'''' and for causing the capacitor to be chargedin a second direction with a current flowing in a second directionduring periods when the first and the second terminals aresimultaneously ''''0,'''' and means including an operational amplifierhaving an input responsive to the direction of flow of the chargingcurrent and the total current energy required to charge the capacitor inresponse to the pulses appearing at the first and second terminals andproviding an output for causing the motor to rotate in the firstdirection in response to the direction of the charging current flow at aspeed proportional to the total current energy required to charge thecapacitor in the first direction and for causing the motor to rotate inthe second direction in response to a direction of the charging currentflow at a speed proportional to the total current energy required tocharge the capacitor in the second direction.